Simulated particles which mimic the behaviours of self-propelling microorganisms have distinct collective properties which depend on their velocities and bottom-heaviness.

From starling aberrations to self-turbulent fluids, ‘active systems’ encompass a wide family of phenomena in which individual objects propel themselves forward, allowing them to display intriguing collective behaviours. On microscopic scales, they are found in groups of living organisms which move around by squirming, and are aligned with Earth’s gravitational fields due to their bottom-heavy mass distributions. Through research published in EPJ E, Felix Rühle and Holger Stark at the Technical University of Berlin find that depending on their properties, these objects collectively spend most of their time in one of two states, between which some intriguing behaviours can emerge.

A Side view of an elastomeric film placed under strain undergoing buckling and wrinkling.

As the demand for flexible electronics grows, researchers must develop robust models of how the materials that comprise them behave under stress.

Flexible circuits have become a highly desirable commodity in modern technology, with applications in biotechnology, electronics, monitors and screens, being of particular importance. A new paper authored by John F. Niven, Department of Physics & Astronomy, McMaster University, Hamilton, Ontario, published in EPJ E, aims to understand how materials used in flexible electronics behave under stress and strain, particularly, how they wrinkle and buckle.

The drag forces experienced by particles which straddle and distort the interfaces between un-mixable fluids are less influenced by the shape of the distortion than previously thought.

Some intriguing physics can be found at the interfaces between fluids, particularly if they are straddled by particles like proteins or dust grains. When placed between un-mixable fluids such as oil and water, a variety of processes, including inter-molecular interactions, will cause the particles to move around. These motions are characterised by the drag force experienced by the particles, which is itself thought to depend on the extent to which they distort fluid interfaces. So far, however, experiments investigating the intriguing effect haven’t yet fully confirmed the influence of this distortion. In new research published in EPJ E, a team led by Jean-Christophe Loudet at the University of Bordeaux, France, showed that the drag force experienced by fluid-straddling particles is less affected by interface distortion than previously believed.

When compared to nanofluids with spherical particles, nanofluids with
anisotropic particles possess higher thermal conductivity and thus offer
a better enhancement option in heat transfer applications. The viscosity
variation of such nanofluids becomes of great importance in evaluating
their pumping power in thermal systems.

EPJ is pleased to announce that January 2020 will see the appointment of two new Editors-in-Chief for EPJ E, Prof Fabrizio Croccolo (Université de Pau et des Pays de l'Adour, France) and Prof Dr Holger Stark (Technische Universität Berlin, Germany).

The Marangoni effect is a popular physics experiment. It is produced when an interface between water and air is heated in just one spot. Since this heat will radiate outwards, a temperature gradient is produced on the surface, causing the fluid to move through the radiation process of convection. When un-dissolvable impurities are introduced to this surface, they are immediately swept to the side of the water’s container. In turn, this creates a gradient in surface tension which causes the interface to become elastic. The structures of these flows have been well understood theoretically for over a century, but still don’t completely line up with experimental observations of the effect. In a new study published in EPJ E, Thomas Bickel at the University of Bordeaux in France has discovered new mathematical laws governing the properties of Marangoni flows.

Experiments and statistical models reveal that the recently developed cancer drug Pixantrone forces itself inside the double helix structure of DNA molecules, then shrinks their backbones.

Because of the harmful side-effects of chemotherapy, and the increasing resistance to drugs found in many cancer cells, it is critical for researchers to continually search for new ways to update current cancer treatments. Recently, a drug named Pixantrone (PIX) was developed, which is far less damaging to the heart than previous, less advanced compounds. PIX is now used to treat cancers including non-Hodgkin’s lymphoma and leukaemia, but a detailed knowledge of the molecular processes it uses to destroy cancer cells has been lacking so far. In a new study published in EPJ E, Marcio Rocha and colleagues at the Federal University of Viçosa in Brazil uncovered the molecular mechanisms involved in PIX’s interactions with cancer DNA in precise detail. They found that the drug first forces itself between the strands of the DNA molecule’s double helix, prising them apart; then compacts the structures by partially neutralising their phosphate backbones.

The deflation of beach balls, squash balls and other common objects offers a good model for distortion in microscopic hollow spheres. This can help us understand the properties of some cells and, potentially, develop new drug delivery mechanisms.

Many natural microscopic objects – red blood cells and pollen grains, for example – take the form of distorted spheres. The distortions can be compared to those observed when a sphere is ‘deflated’; so that it steadily loses internal volume. Until now, most of the work done to understand the physics involved has been theoretical. Now, however, Gwennou Coupier and his colleagues at Grenoble Alps University, France have shown that macroscopic-level models of the properties of these tiny spheres agree very well with this theory. The new study, which has implications for targeted drug delivery, was recently published in EPJ E.

Mechanism of formation of an early vertebrate embryo. Each of the rings of cells in the round blastula (shown in colours) forms into a different part of the embryo or placenta.

Electrical stimulation of early chicken embryos has shed light on the process through which the limbs of all vertebrates are formed.

Every vertebrate, whatever its eventual form, starts embryonic life in the same way – as a hollow ball or disc of cells called a blastula. In theory, knowing the mechanism through which the blastula is formed into the shape of an animal could help correct defects and even, one day, regenerate body parts. But evolution and genetics are of little help in understanding this process. Now, however, Vincent Fleury and Ameya Vaishnavi Murukutla from Université Paris Diderot, Paris, France have used experiments with chicken embryos to propose a mechanism for vertebrate limb formation. These findings have been published in the journal EPJ E.

The critical region in the phase diagram of condensed matter systems such as fluids or fluid mixtures is characterized by the anomalous behaviour of specific thermodynamic properties. In a new review article published in EPJE, Patricia Losada-Pérez (Department of Physics, Université Libre de Bruxelles) describes recent progress in the understanding of the behaviour of two intimately related properties, the dielectric constant ε and the refractive index n, when approaching the liquid-liquid critical point in binary liquid mixtures.